Functional but not obligatory link between microsaccades and neural modulation by covert spatial attention

Abstract

Covert spatial attention is associated with spatial modulation of neural activity as well as with directional biases in fixational eye movements known as microsaccades. We studied how these two ‘fingerprints’ of attention are interrelated in humans. We investigated spatial modulation of 8-12 Hz EEG alpha activity and microsaccades when attention is directed internally within the spatial layout of visual working memory. Consistent with a common origin, spatial modulations of alpha activity and microsaccades co-vary: alpha lateralisation is stronger in trials with microsaccades toward versus away from the memorised location of the to-be-attended item and occurs earlier in trials with earlier microsaccades toward this item. Critically, however, trials without attention-driven microsaccades nevertheless show clear spatial modulation of alpha activity – comparable to trials with attention-driven microsaccades. Thus, directional biases in microsaccades correlate with neural signatures of spatial attention, but they are not necessary for neural modulation by spatial attention to be manifest.

Microsaccades transiently lateralise EEG alpha activity

“…Whatever the exact physiological origins of the here-reported microsaccade-locked transient alpha lateralisation, our results – together with those before us 10,14–17,33,49–51 – carry a relevant practical implication. They highlight the importance of considering microsaccades when reporting neural modulation by specific task variables.…”

“…Like here, we found that alpha lateralisation and microsaccade direction correlated – when microsaccades occurred. However, we also found that microsaccades were not necessary, since task-driven alpha lateralisation was preserved in trials without microsaccades 10 (see also 52 ). The present report suggests that explorations of this type should be adopted more widely.…”

“…This is because conditional differences in microsaccades (such as biases in microsaccade direction [6][7][8][9][10] ) may account for conditional differences in neural activity (such as the spatial modulation of alpha activity [19][20][21][22] ) and mislead interpretation. Following this logic, we recently interrogated whether goal-driven biases in microsaccade direction can fully account for the goal-driven lateralisation of EEG-alpha activity by spatial attention 10 . Like here, we found that alpha lateralisation and microsaccade direction correlated -when microsaccades occurred.…”

“…The sample size was based on previous publications from the lab that had similar designs and focused on similar neural signatures (for example see 54 ). As in our two prior articles that also focused on the eye-tracking data from this dataset (Experiment 1 in 9 and 10 ), two participants were excluded due to their poor quality of eye-tracking data. The experimental procedures were reviewed and approved by the Central University Research Ethics Committee of the University of Oxford.…”

Internal selective attention is delayed by competition between endogenous and exogenous factors

“…First, although attention-related modulations of cortical and subcortical processing are larger during trials containing microsaccades towards the location of a (covertly) attended stimulus, clear attention-related modulations are also observed in the absence of microsaccades (Yu et al, 2022;Liu et al, 2022; though see Lowet et al 2018 for a contradictory result). Second, any of the three models examined in the current study (i.e., retro-capture, automatic refreshing, or delayed selection) could have produced the delays in microsaccade biases reported by van Ede et al ( 2020).…”